FEATURE
reefs
With corals at risk, scientists
attempt underwater rehab
By Amy McDermott
C
oral reefs are bustling cities beneath tropical, sunlit
waves. Thousands of colorful creatures click, dash
and dart, as loud and fast-paced as citizens of any
metropolis.
Built up in tissue-thin layers over millennia, corals are
the high-rise apartments of underwater Gotham. Calcium
carbonate skeletons represent generations of tiny invertebrate
animals, covered in a living layer of colorful coral polyps. Their
structures offer shelter, and for about 114 species of fish and
51 species of invertebrates, those coral skyscrapers are lunch.
Important as they are, corals are in jeopardy. Warming
oceans are causing more and more corals to bleach white and
18 SCIENCE NEWS | October 29, 2016
become vulnerable to destruction. A
A coral fluoresces
purple (left), perhaps
prolonged spike in temperatures, just
as a sunscreen
1 to 2 degrees Celsius, is enough to kill
defense for colorless
the marine animals. Greenhouse gas
polyps, in a photo
taken September 12
emissions also acidify the water, disof a bleached reef
solving the calcium skeletons. In some
near Okinawa, Japan.
countries, fishermen use dynamite
to catch fish, leaving behind coral rubble. Today, more than
60 percent of the world’s reefs are at risk of disappearing.
Threats to reefs have “dramatically escalated in the last few
decades,” says marine scientist Peter Harrison of Southern
Cross University in Lismore, Australia. He has studied corals
for three decades. “In my time as a reef researcher,” Harrison
says, “I’ve seen it get worse, firsthand.”
Thirty years ago, massive coral bleachings were unheard of.
Today, reefs are suffering through a third global bleaching event
since 1998. With high ocean temperatures dragging on since
© XL CATLIN SEAVIEW SURVEY/UNDERWATER EARTH
REBUILDING
Honolulu in June, Harrison’s team reported early promising
results of its effort to flood damaged reefs in the Philippines
with tiny coral larvae.
What works on one reef won’t necessarily save another. So
researchers are testing an arsenal of options to rescue a diversity of underwater communities.
A different story
In the early 1980s, Harrison was a graduate student at James
Cook University in Townsville, Australia, working on the Great
Barrier Reef. At the time, textbooks taught that most corals
reproduce by brooding: Fertilization occurred inside the body
and larvae were released into the water to replenish reefs yearround. But Harrison witnessed something very different. For a
few nights around a full moon in springtime, corals spawned,
spewing eggs and sperm into the water to be externally fertilized. The sea was covered in a pink, oily slick.
“We found the corals hadn’t read the textbooks,” Harrison
says. Eggs and sperm were meeting outside of the coral bodies, and larvae were developing while drifting in the currents.
That discovery spurred a cascade of studies on coral reproduction that led to the modern understanding that many
corals reproduce only once or twice a year, in coordinated mass
releases of eggs and sperm. Most of the resulting larvae die or
drift out to sea, Harrison says. Only a small fraction survive
to adulthood. Even so, mass spawns are “how reefs replenish
themselves over time,” he says.
Just after Harrison’s discovery, the Great Barrier Reef,
and then reefs around the globe, experienced bleaching on
a massive scale. Normally, tiny algae live inside coral polyps.
The algae make sugar and other nutrients for the coral, and
can give polyps their characteristic bright colors. But when
temperatures spike, algae become toxic. Corals spit out their
partners, bleach white and can die if temperatures don’t cool
enough for the algae to return (SN Online: 10/8/15).
Corals worldwide were bleaching more often and more
severely than had been recorded in the past. Scientists began
2014, this summer marked the longest and most widespread to worry that reefs were in trouble. Some researchers, like Dave
episode of worldwide coral bleaching on record (SN: 7/23/16, Vaughan, who manages the Coral Reef Restoration program at
p. 5). Australia has been hit especially hard. More than 80 percent the Mote Tropical Research Laboratory in Summerland Key,
of the northern part of the Great Barrier Reef is bleached Fla., took action.
In those days, Vaughan was a fish farmer,
and close to half of those corals have died,
according to a report in April from Australia’s This summer marked raising saltwater fish species in captivity. He
National Coral Bleaching Taskforce.
the longest and most began growing corals for tropical aquarium
tanks. At the time, all the corals in the aquarAs reefs take a nose dive, scientists from
widespread episode ium trade were taken from the wild, Vaughan
Hawaii to the Philippines and the Caribbean
of worldwide coral says. He started growing coral species in
are scrambling to save corals. Approaches that
were once considered radical are “now seen as
bleaching on record. captivity as an environmentally friendly
alternative.
necessary in some places,” says coral biologist
One day, Philippe Cousteau, grandson of legendary aquanaut
Ruth Gates of the Hawaii Institute of Marine Biology on Oahu.
In Florida, researchers are restoring reefs with tiny coral frag- Jacques, toured the operation. When the young Cousteau saw
ments. In Hawaii, Gates is scouring the water for stress-tolerant that Vaughan was raising corals for aquariums, “he shook his
corals and experimenting in the lab to breed the hardiest indi- head,” Vaughan remembers, “and said ‘Dave, if you could do
viduals. At the 13th International Coral Reef Symposium in this for the aquarium trade, you can do this for the reef.’ ”
www.sciencenews.org | October 29, 2016 19
Stressed out
Changing conditions, such
as rising ocean temperatures and local pollution,
can kill reefs by bleaching
corals. Here’s how tough
times turn reefs white.
SOURCE: NOAA CORAL REEF
CONSERVATION PROGRAM
Healthy coral
Stressed coral
Bleached coral
Photosynthetic
algae (dark
green dots) live
in coral polyps
and make
nutrients that
corals eat.
Algae give corals
their characteristic color. Under
stress, corals
reject the algae
and begin to
fade to white.
If conditions
don’t improve
enough for
algae to return,
corals can starve
or succumb to
disease.
In those earliest days, most scientists were tackling small- labor-intensive, and therefore very expensive. And, Harrison
scale reef damage caused by dropped anchors or boat ground- says, they rely on cloning.
When one coral is broken into fragments, to be fattened
ings, Vaughan says. To repair that kind of minor damage,
scientists began breaking 3- to 5-centimeter fragments from up and then planted around a reef, each chunk is genetically
healthy corals on a neighboring reef and transplanting the identical. All those pieces have the same DNA blueprint to fight
infection and to deal with stress. Unlike natural reefs, where
chunks in damaged spots.
Cousteau’s visit convinced Vaughan that he should try restor- individuals are genetically distinct and have different vulnering reefs. While doing so, 11 years ago, Vaughan made a game- abilities, cloned corals share the same weaknesses.
“People have spent years growing coral gardens only to have
changing discovery: Tinier fragments of coral, only 1 centimeter
long, repair themselves 25 to 40 times as fast as scientists had them wiped out by the next bleaching event,” Harrison says.
With more diversity, he adds, some of those corals might have
ever recorded corals growing.
Today Vaughan’s team is spreading many of these microfrag- survived. In a warmer world where bleaching and disease will
ments over the surface of dead coral skeletons in the Florida probably become more common, “genetic diversity equals
Keys. As those bits fuse back together, they create a fast-grow- resilience.”
To address the diversity issue, Vaughan and Page are raising
ing “skin” over an otherwise dead reef. Condemned buildings
20 to 30 genetic variants of each coral species, to be planted
are refurbished rather than razed.
The hope is that thousands of microfragments will carpet a around the reef. They are also collecting eggs and sperm from
small reef in two to three years, says Chris Page, a biologist at wild colonies of four coral species to grow on Summerland Key.
Harrison has been thinking about genetic diversity ever
Mote Marine Laboratory working with Vaughan. That’s super
since the early 1980s, when he saw corals spewing sperm and
fast. “There’s no way that’s happening in nature,” Page says.
Vaughan’s team is cultivating 17 species for microfragmenta- eggs into the ocean. Few of the resulting larvae would survive.
tion in large troughs on land, with seawater running through Many would drift away and most would die. All while Harrison
them. He is focused on the top six slow-growing massive spe- saw reefs in decline.
What if, he wondered, scientists could take millions of those
cies that create the foundation of the reef. Some can live for
centuries, mounded into boulders the
size of a truck.
Coral microfragments grow on round pucks in nursery troughs (left) on Florida’s Summerland Key
The Florida researchers plunged in 2016. Reef scientist Dave Vaughan (right) plants microfragments from the nursery to restore
reef-building corals at the southern tip of Key West.
their first 200 microfragments into
the ocean three years ago, at two sites
in a nearshore coral reef off Big Pine
Key, Fla. The colonies are now six
to eight times as large as they were
at planting and have begun to fuse
together into areas about the size of a
5-gallon bucket lid. Since then, Vaughan
and Page have planted close to 10,000
microfragments in the wild. “People
were looking for some glimmer of light,”
Vaughan says. “And restoration is turning out to be that in a big way.”
Seeds of reefs
Fragmentation and the newer microfragmentation are both time- and
20 SCIENCE NEWS | October 29, 2016
TOP: E. OTWELL: BOTTOM, FROM LEFT: C. PAGE; CONOR GOULDING/MOTE MARINE LABORATORY
FEATURE | REBUILDING REEFS
diverse coral larvae and help them settle onto reefs to replenish ailing ecosystems?
Other researchers asked themselves the same question. In
the late 1990s and from 2007 to 2009, two teams, in Australia
and Palau, released coral larvae onto healthy reef areas in mesh
tents pitched over the seabed. In both studies, thousands of larvae settled under the tents, many more than scientists would
have seen naturally.
But those early results may have been misleading. Most
of the early settlers in Palau died within 30 weeks. Flooding
the reef with larvae didn’t make a lasting difference in coral
numbers. Maybe, the researchers speculated, settlers were
too crowded, which meant swamping reefs with larvae made
no sense.
Harrison wasn’t ready to give up. Even though most of the
new settlers had died, those studies were done on healthy reefs,
he says. In battered areas, where some baby corals might naturally drift in, but not enough for the reef to self-heal, a flush of
larvae could be a shot in the arm.
The idea was to find a badly damaged reef, where the worst
problems, such as blast fishing, had stopped. Harrison would
bring a few of the reef’s mature, sexually active corals to the
lab, persuade them to release sperm and eggs in aquarium
tanks, and then take more than a million of their larvae back
out to the reef. The plan was to saturate the environment with
settling babies, as adult corals would have done in healthier
days.
In 2013, Harrison’s team, led by graduate student Dexter
dela Cruz, began a small pilot experiment in the Philippines Peter Harrison (top, right) and Dexter dela Cruz (left) place millions
of Acropora tenuis larvae into a mesh tent in April 2016 to rehabilitate
at a reef called Magsaysay, where nearly two decades of fishing Magsaysay, a degraded reef in the Philippines. When those larvae become
with explosives had taken a toll. Blast fishing is “like hitting the adults, they spawn, like this A. tenuis on the Great Barrier Reef (bottom).
reef with a sledgehammer,” Harrison says. Magsaysay’s large
foundational corals were blown to bits. A once-vibrant city was Winning corals
now a wasteland.
Getting more larvae onto damaged reefs is the first step,
By 2013, the blast fishing had stopped, but Magsaysay wasn’t Harrison says. But some individuals are stronger and more
recovering on its own. So Harrison’s team brought in larvae stress-tolerant than others. As they grow up, these “winners”
from a species of fast-growing, purple-tipped coral,
distinguish themselves by surviving.
called Acropora tenuis, collected from a nearby
Across the Pacific from Magsaysay, biologist Gates is
healthier reef. The scientists released more than
studying winners. Rows of indoor and outdoor aquara million larvae into floorless mesh tents pitched
iums gurgle in her lab on Coconut Island, off Oahu’s
under­water over the reef. After five days, Harrison’s
windward shore. Those tanks are full of Montipora
percent
team removed the mesh enclosures.
capitata, a local and fast-growing coral collected from
Fraction of the
Over the next six months, most of the tiny coral reefs damaged in the patchy reefs surrounding the island.
the Philippines
settlers died. But, by the nine-month mark, the
In 2014 and 2015, unusually warm water hit
remaining populations had stabilized. Scientists expected Hawaii. Under stress, many corals rejected their symbiotic
more of the juvenile corals to die, but “incredibly and algae, then blanched from a healthy brown to white; some died.
extraordinarily,” Harrison says, none have. At 3 years old, the
Gates’ team patrolled the reefs around the island during and
juvenile corals have reached sexual maturity and are now the after the bleaching, in search of hardy M. capitata individuals
size of dinner plates. In June, dela Cruz presented the find- that stayed brown, even in hot water. The scientists are also
ings in Honolulu.
interested in M. capitata that bleached, but then recovered.
For slower-growing corals, Harrison’s approach will take Gates equates the work to professional sports scouting, “out
extra patience. But for fast-growers like A. tenuis, reseeding at high schools, looking for the best athletes.”
larvae could be a quick and affordable way to help severely
When she finds top performers, Gates brings them to
damaged reefs bounce back.
her lab to run them through their paces, exposing each
FROM TOP: KERRY CAMERON; P. HARRISON
54
www.sciencenews.org | October 29, 2016 21
FEATURE | REBUILDING REEFS
Ruth Gates snorkels by bleached (left) and healthy M. capitata (right) on
Oahu, Hawaii. She selectively breeds resilient corals.
Approaches like microfragmentation could help super colonies
mature super fast. Then, Gates says, “we would have a strategy
to get the reef producing its own offspring quite quickly.”
No two approaches to saving reefs are the same, which is
probably a good thing. Coral fragmentation, reseeding and
selective breeding each have their pros and cons.
“The assumption that one size will fit all is completely
flawed,” Gates says. What might work on the Florida coast
wouldn’t necessarily work in the Pacific. Like far-flung cities,
each reef has different needs and priorities. Their communities of coral vary as do the threats they face. Some problems,
like warming oceans, are global in scope. Others, like pollution
from roads and agricultural runoff, overfishing and dynamite
fishing, are often more localized. Rehabilitation approaches
will vary, depending on the type and severity of damage, and
how the mosaic of coral species might respond.
Across the globe, “will the things that we do be different?”
Gates asks. “Absolutely.”
Rather than competing, Gates, Vaughan and Harrison
are working toward a common goal: to find the right mix of
approaches to support the reefs so they no longer need human
help. s
Explore more
Bleached corals (left) and healthy ones (right) fluoresce differently
under a laser scanning confocal microscope. Glow patterns may help
scientists identify super corals in the future.
22 SCIENCE NEWS | October 29, 2016
ss Peter Harrison, Ronald Villanueva and Dexter dela Cruz.
“Coral reef restoration using mass coral larval reseeding.”
Australian Centre for International Agricultural Research.
June 20, 2016. bit.ly/coralreseeding
ss Zac H. Forsman et al. “Growing coral larger and faster:
micro-colony-fusion as a strategy for accelerating coral
cover.” PeerJ. October 20, 2015.
ss Global Coral Bleaching: www.globalcoralbleaching.org
TOP: VULCAN INC.; BOTTOM, BOTH: KATIE BAROTT
pro-performer to different temperatures and pH levels in seawater tanks. Some conditions re-create today’s oceans, while
others mimic future warm and more acidic seas.
Today, Gates is breeding the strongest corals (her first
batch of babies was born in June). She hopes that top performers will have “extremely talented kids” that inherit their
parents’ strengths. It’s too soon to tell how the new corals will
do once they’re planted out on the reef.
“We’re trying to give corals a leg up,” she says. Reefs healthy
enough to survive without human intervention are the ultimate aim. In the next five years, the researchers plan to branch
out from M. capitata to look for super corals of all five species
found in the bay surrounding Coconut Island.
It would be ideal to find those super corals before the next
big bleaching event. But for that, the researchers need another
sign of resilience. That sign, Gates says, could be hidden in the
way corals glow.
Some coral animals, and their symbiotic algae, are loaded
with fluorescent proteins that absorb incoming light, then spit
it back out by glowing. It’s unclear what fluorescent proteins
do for corals; they may be a kind of sun block, protecting corals
from the intense light in shallow seas, or a form of camouflage
or part of the immune system.
Stress affects corals’ glowing proteins and changes their
fluorescence patterns. In the Pacific and Indian Ocean species
Acropora yongei, for instance, researchers reported in 2013 in
Scientific Reports that the concentration of green fluorescent
protein fell with temperature stress before bleaching and the
coral glowed less intensely. In an earlier study, prolonged high
temperatures changed the ratio of green to orange fluorescence in the endangered Caribbean coral Orbicella faveolata.
Gates expects that under stress, super corals will keep their
healthy fluorescence patterns much longer than corals that are
bleaching. One next step, Gates says, is to stress out tiny pieces
of coral and watch what happens under a very powerful laser
scanning confocal microscope. She’ll expose nubbins of coral
to acidifying water or increasing temperatures in a petri dish.
The microscope will pick up the fluorescence of the nubbins
and may indicate which corals will stay healthy the longest.
Once scientists can identify the hardiest corals, they can
combine selective breeding with other rehab techniques.